1. Field of the Invention
The present invention relates generally to a method and apparatus for monitoring video receivers, and more particularly to a method and apparatus for determining the channel reception and the broadcast signal source of the signal being displayed by a monitored receiver.
2. Description Of The Prior Art
Various arrangements have been employed to determine the channel to which a television receiver is tuned. A disadvantage of many known monitoring arrangements is that an internal connection to the television receiver is required. For example, U.S. Pat. No. 3,973,206 issued to Haselwood, et al. on Aug. 3, 1976 discloses a method of determining channel tuning by monitoring the varactor diode tuning voltage and thus, required internal connections in the television receiver.
Another method for determining channel tuning disclosed in U.S. Pat. No. 4,425,578 issued to Haselwood et al. on Jan. 10, 1984 utilizes a signal injection source and a detector/receiver arranged to detect the combined signal from the injection signal source and a video carrier to which the video receiver is tuned. A significant drawback of signal injection monitoring arrangements is potential interference with the functional operation of the video receiver being monitored.
Other known arrangements have utilized a local oscillator frequency measurement of the monitored receiver to determine channel tuning. However, known local oscillator measurements are prone to errors caused by extraneous signals and can interfere with normal operation of the monitored video receiver.
A further difficulty with such conventional arrangements results from the increasing use of video cassette recorders and cable and pay television systems in conjunction with the television receiver requiring monitoring of the associated tuner device. Access to the associated tuner device may not be possible; however, where access is possible, the overall complexity of conventional monitoring systems is substantially increased.